Structure in the motions of the fastest halo stars

Fiorentin, P. Re; Helmi, Amina; Lattanzi, M. G.; Spagna, A.

doi:10.1051/0004-6361:20052911

Cited by 28 publications

(38 citation statements)

References 37 publications

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“…By comparing the observed distribution of stars in the L z − L ⊥ space with Monte Carlo simulations of smooth, non rotating stellar halos, the over-density found at (L z , L ⊥ ) (1000, 2000) kpc km s −1 was shown to be significant and was interpreted as evidence of an accreted stream, known as the "Helmi stream" after this discovery. Other studies have subsequently confirmed the presence of this overdensity in the L z − L ⊥ space, confirming its extra-galactic nature (Chiba & Beers 2000;Re Fiorentin et al 2005;Dettbarn et al 2007;Kepley et al 2007;Klement et al 2009;Smith et al 2009;Re Fiorentin et al 2015) and concluding that approximately 5% of the local stellar halo should be made of stars belonging to this stream. Apart from the Helmi stream, possible others have potentially been detected in the L z − L ⊥ plane (see, for example Kepley et al 2007;Smith et al 2009;Re Fiorentin et al 2015).…”

Section: On the L ⊥ -L Z Spacementioning

confidence: 62%

“…2-4, has been performed selecting stellar particles in restricted solar volumes (3 kpc in radius). These are the typical volumes over which the kinematic search of stellar streams has been focused until now (Helmi et al 1999;Kepley et al 2007;Morrison et al 2009;Smith et al 2009;Re Fiorentin et al 2005. In the coming years, with Gaia and spectroscopy-related surveys such GALAH, WEAVE, and 4MOST, we will have an almost complete view of stars up to ∼3 kpc from the Sun: distances, kinematics, ages and detailed abundances.…”

Section: Leaving the Solar Volume: Kinematic Detection Of Streams On mentioning

confidence: 99%

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On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

Jean-Baptiste

Matteo

Haywood

et al. 2017

A&A

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The ΛCDM cosmological scenario predicts that our Galaxy should contain hundreds of stellar streams in the solar vicinity, fossil relics of the merging history of the Milky Way and more generally of the hierarchical growth of galaxies. Because of the mixing time scales in the inner Galaxy, it has been claimed that these streams should be difficult to detect in configuration space but can still be identifiable in kinematic-related spaces like the energy/angular momenta spaces, E − L z and L ⊥ − L z , or spaces of orbital/velocity parameters. By means of high-resolution, dissipationless N-body simulations containing between 25 × 10 6 and 35 × 10 6 particles, we model the accretion of a series of up to four 1:10 mass ratio satellites then up to eight 1:100 satellites and search systematically for the signature of accretions in these spaces. The novelty of this work with respect to the majority of those already published is our analysis of fully consistent models, where both the satellite(s) and the Milky Way galaxy are "live" systems, which can react to the interaction and experience kinematical heating, tidal effects and dynamical friction (the latter, a process often neglected in previous studies). We find that, in agreement with previous works, all spaces are rich in substructures, but that, contrary to previous works, the origin of these substructures -accreted or in-situ -cannot be determined for the following reasons. In all spaces considered (1) each satellite provides the origin of several independent over-densities; (2) over-densities of multiple satellites overlap; (3) satellites of different masses can produce similar substructures; (4) the overlap between the in-situ and the accreted population is considerable everywhere; and (5) in-situ stars also form substructures in response to the satellite(s') accretion. These points are valid even if the search is restricted to kinematically-selected halo stars only. As we are now entering the "Gaia era", our results warn that extreme caution must be employed before interpreting over-densities in any of those spaces as evidence of relics of accreted satellites. Reconstructing the accretion history of our Galaxy will require a substantial amount of accurate spectroscopic data, that, complemented by the kinematic information, will possibly allow us to (chemically) identify accreted streams and measure their orbital properties.

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Section: On the L ⊥ -L Z Spacementioning

confidence: 62%

Section: Leaving the Solar Volume: Kinematic Detection Of Streams On mentioning

confidence: 99%

On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

Jean-Baptiste

Matteo

Haywood

et al. 2017

A&A

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“…In particular, Klement et al (2009) already showed that the streams 'C2', 'C3' and 'S 3 ' are not only kinematically and chemically connected, but also spatially coherent, similar to a small overdensity at (R, z) ≈ (9.5, 0.8) kpc described by Juric et al (2008). Other streams with a common origin might be the RHLS and H99 groups (Re Fiorentin et al 2005), R2 and KFR08 (Klement et al 2009) and the S 3 streams from Dettbarn et al (2007) and Klement et al (2009), respectively. Furthermore, relations between halo streams and certain globular clusters have been suggested in several instances, based on their common position in the IoM-space. In particular, relations have been suggested between SKOa and the clusters NGC 5466, NGC 6934, NGC 7089/ M2 and NGC 6205/ M13 (Smith et al 2009).…”

Section: A Census On the Currently Known Halo Streamsmentioning

confidence: 73%

“…Indeed, the classical integrals of motion have been used successfully for finding tidal debris in the solar neighborhood Chiba and Beers 2000;Re Fiorentin et al 2005;Kepley et al 2007;Smith et al 2009); however, some limitations have to be considered (pointed out by Helmi et al 2006): First, the total angular momentum |L| is only strictly conserved in a spherical potential which is not the case for the Milky Way. However, this seems to be a minor point, because even for stars that move in axisymmetric flattened potentials, |L| is approximately conserved and similar to the third integral I 3 , for which no analytic expression exists (Binney and Tremaine 2008, Sect.…”

Section: Integrals Of Motion and Action-angle Variablesmentioning

confidence: 99%

“…Although this meant a sample size three times as large as H99's, they found practically the same number of stream members. The Beers et al catalog was re-examined by Re Fiorentin et al (2005), but now concentrating on the classical search strategy for moving groups, namely picking out stars with strong correlations in velocity space. Among the 5% of the fastest moving halo stars, Re Fiorentin et al found a kinematic group consisting of 3 stars with similar angular momenta, but somewhat lower binding energy than the H99 streams.…”

Section: The Helmi Streammentioning

confidence: 99%

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Halo streams in the solar neighborhood

Klement

2010

Astron Astrophys Rev

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The phase-space structure of our Galaxy holds the key to understand and reconstruct its formation. The CDM model predicts a richly structured phase-space distribution of dark matter and (halo) stars, consisting of streams of particles torn from their progenitors during the process of hierarchical merging. While such streams quickly loose their spatial coherence in the process of phase mixing, the individual stars keep their common origin imprinted into their kinematic and chemical properties, allowing the recovery of the Galaxy's individual "building blocks". The field of Galactic Archeology has witnessed a dramatic boost over the last decade, thanks to the increasing quality and size of available data sets. This is especially true for the solar neighborhood, a volume of 1-2 kpc around the sun, where large scale surveys like SDSS/SEGUE continue to reveal the full 6D phase-space information of thousands of halo stars. In this review, I summarize the discoveries of stellar halo streams made so far and give a theoretical overview over the search strategies imployed. This article is intended as an introduction to researchers new to the field, but also as a reference illustrating the achievements made so far. I conclude that disentangling the individual fragments from which the Milky Way was built requires more precise data that will ultimately be delivered by the Gaia mission.

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Tidal Streams in the Local Group and Beyond

Newberg¹,

Carlin²

2016

Astrophysics and Space Science Library

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The stellar debris structures that have been discovered around the Milky Way and other galaxies are thought to be formed from the disruption of satellite stellar systems-dwarf galaxies or globular clusters-by galactic tidal fields. The total stellar mass in these structures is typically tiny compared to the galaxy around which they are found, and it is hence easy to dismiss them as inconsequential. However , they are remarkably useful as probes of a galaxy's history (as described in this chapter) and mass distribution (covered in a companion chapter in this volume). This power is actually a consequence of their apparent insignificance: their low contribution to the overall mass makes the physics that describes them both elegant and simple and this means that their observed properties are relatively easy to understand and interpret.

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Structure in the motions of the fastest halo stars

Cited by 28 publications

References 37 publications

On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

Halo streams in the solar neighborhood

Tidal Streams in the Local Group and Beyond

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